Other Comprehensive Income (Loss) (Components Of Accumulated Other Comprehensive Income (Loss), Net Of Tax, In The Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		$ 9,132,925			$ 9,132,925
Current period change	$ 566,888		$ 171,209		268,984	$ 417,655
Balance	9,286,299		8,836,817		9,286,299	8,836,817
URA(D) On Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	56,426	304,425	51,851	$ (179,392)	304,425	(179,392)
Current period change	544,496		197,312		296,496	428,729
Balance	600,922	56,426	247,741	51,851	600,922	247,741
URA(D) On Securities OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Current period change			(1,422)			(1,596)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(252,541)	(201,717)	(201,695)	(215,747)	(201,717)	(215,747)
Current period change	20,586		(25,832)		(30,238)	(11,780)
Balance	(231,955)	(252,541)	(227,527)	(201,695)	(231,955)	(227,527)
Benefit Plan Net Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(73,636)	(74,556)	(66,267)	(67,418)	(74,556)	(67,418)
Current period change	1,806		1,151		2,726	2,302
Balance	(71,830)	(73,636)	(65,116)	(66,267)	(71,830)	(65,116)
Accumulated Other Comprehensive Income (Loss), Net of Deferred Income Taxes [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(269,751)	28,152	(216,111)	(462,557)	28,152	(462,557)
Current period change	566,888	(297,903)	171,209	246,446
Balance	$ 297,137	$ (269,751)	$ (44,902)	$ (216,111)	$ 297,137	$ (44,902)